| Gold and platinum have played an essential role in electronic materials,catalysts,aerospace industry and other high-tech fields because of their excellent performance and unique physical and chemical properties.However,due to the depletion of mineral resources and the limitation of mining technology,the production of gold and platinum is difficult to meet the increasing needs of people,forcing people to shift their attention to secondary resources rich in precious metals to solve the problems caused by the lack of gold and platinum.Ionic liquids have excellent selectivity,extremely low vapor pressure and relatively low toxicity.In recent years,they have been regarded ionic liquids as a novel type of green extractant by many researchers and widely used in the field of extraction and separation.However,ionic liquids often have large mass transfer resistance between the two phases due to their high viscosity in the extraction process.In the actual extraction process,a large number of organic solvent is needed as diluents,which will undoubtedly reduce the green properties of ionic liquids and contradict the concept of sustainable development.Therefore,the development of green extraction system based on ionic liquids has gradually become the focus of research.In this paper,three new types of nitrogen-containing ionic liquids were,and a new green extraction system consisting of ionic liquids and water is constructed.Under the condition of no organic solvent,gold and platinum can be rapidly separated from acidic medium,details are as follows:Firstly,a novel quaternary ammonium ionic liquid([Ach][Tf2N])was synthesized and applied to the extraction and separation of Au(III)in acidic medium.In this extraction system,[Ach][Tf2N]can be employed as both extractant and solvent in the extraction process.By modulating various parameters,the extraction behavior of Au(III)under various conditions was investigated.The result shows that it is more suitable for the extraction of Au(III)under high salinity and lower acidity conditions,and the extraction efficiency can reach 98.98%in 5 min.The extraction compounds were characterized and analyzed by UV-Vis spectra,13C NMR spectra and FT-IR spectra.The extraction mechanism between[Ach][Tf2N]and AuCl4-was proved to be anion exchange mechanism.The gold loaded in ionic liquid phase was easily stripped completely by 1 mL 0.05 mol·L-1 CS(NH2)2/0.1 mol·L-1 HCl solution.At the same time,[Ach][Tf2N]also possesses excellent selectivity for Au(?)in the mixed metal solutions.Furthermore,its operating conditions combination:ionic liquid dosage,the concentration of HCl and NaCl were optimized to 0.55 g,0.5 mol·L-1 and 2.5 mol·L-1 by response surface methodology(RSM),respectively.Hence,the[Ach][Tf2N]was regarded as a potential extractant for gold recovery from secondary resources.Secondly,two UCST quaternary ammonium ionic liquids were designed and synthesized,and the ionic liquid-water binary extraction system was constructed by using its temperature-controlled characteristics to realize the homogeneous liquid-liquid extraction of Au(?)from acidic medium.The effects of inorganic salts cations,anions and inorganic acids on the phase transformation behavior of the temperature-controlled extraction system were investigated.By comparing the hydrophobicity of the two ionic liquids,the succinylcholine bis(trifluoromethylsulfonyl)-imide([Suc][Tf2N]2)was selected for the further extraction of Au(?).Then,a comparison between traditional liquid-liquid extraction and homogeneous liquid-liquid extraction was made during the process of optimization of various extraction parameters.Furthermore,the anion exchange mechanism of the extraction process was confirmed by UV-vis,FT-IR,13C NMR characterization.The[Suc][Tf2N]2 thermoregulated system presented an excellent selectivity for Au(?)from multimetallic ions coexisting solution.Finally,Au(?)loaded in the ionic liquid phase was almost completely stripped to obtain elemental gold using oxalic acid solution.The extraction ability of[Suc][Tf2N]2 remains stable after five cycles through the regeneration of ionic liquids by supplementing anions.The extraction efficiency of Au(?)using regenerated ionic liquid still maintain a surprisingly stability after five turns of cycling experiments.Hence that,the dicationic ionic liquid[Suc][Tf2N]2 was regarded as a green and high efficiency extractant for the recovery of gold.Finally,a novel UCST-type amino-functionalized ionic liquid-carbamoylcholine bis(trifluoromethylsulfonyl)imine([Car][Tf2N])was synthesized,and the[Car][Tf2N]-H2O thermomorphic system was designed to separate Au(?)and Pt(?)from acidic medium by homogeneous liquid-liquid extraction.The cloud point of[Car][Tf2N]and water at different mass ratios was measured by experiments,and the phase diagram was drawn.Then,the correlation relationship between the cloud points of[Ach][Tf2N]?[Suc][Tf2N]2?[Car][Tf2N]and their electrostatic potential was proved by quantum chemical calculation.The effects of extractant dosage,acidity,salinity and temperature on the extraction behavior of Au(?)and Pt(?)were investigated,and the optimum extraction conditions were obtained.The extraction mechanisms of Au(?)and Pt(?)were proposed as an anion exchange mechanism by analyzing the UV-Vis spectra,13C NMR spectra and FT-IR spectra of the extracted compounds.Finally,the gold loaded in ionic liquid phase can be stripped by oxalic acid,and platinum was stripped by thiourea solution. |
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